Many algorithms for routing in sensor networks exploit greedy
forwarding strategies to get packets to their destinations. In
this paper we study a fundamental difficulty such strategies face:
the ``local minimum phenomena'' that can cause packets to get
stuck. We give a definition of stuck nodes where packets may get
stuck in greedy multi-hop forwarding, and develop a local rule,
the TENT rule, for each node in the network to test whether
a packet can get stuck at that node. To help the packets get out
of stuck nodes, we describe a distributed algorithm,
BOUNDHOLE, to build routes around "holes", which are
connected regions of the network with boundaries consisting of all
the stuck nodes. We show that these hole-surrounding routes can be
used in many applications such as geographic routing, path
migration, information storage mechanisms and identification of
regions of interest.